What programs allow me to manually sync individual music files from macOS to iOS and iPadOS?

I use Music.app, but not the Apple Music subscription service. All my music is local files on my computer. For some time now, syncing my iPhone and iPad via Finder fails to sync changes I've made to my music library to the mobile devices. It will not see newly added files or metadata changes and will not sync them. Sometimes it simply ignores them. Sometimes it gives me an error like this after something as simple as changing the track number in the file's metadata, when the file is just an AAC file that is already on the phone and playing fine: > Some items, including "Example Song", were not copied to the iPhone "Example iPhone" because they cannot be played on this iPhone. The only way I've found to force my library to sync is to completely delete my library on the Mac, create a new one, and toggle syncing on each mobile device, so that it erases the contents and re-syncs the entire library. This takes forever and also causes things like "date added" to be lost forever. I've been looking for an alternative since I've given up hope that Apple will fix this. They don't care about anything but the Apple Music subscription service. The closest solution I found was [Doppler](https://brushedtype.co/doppler/), a music player for both macOS and iOS that has its own syncing mechanism, completely bypassing the broken sync in Music.app/Finder. However, there are a few downsides which have me continuing to look for another option, in order of importance: * The sync works by putting your music files in a dedicated directory in the Files app on the mobile device. This means that the device doesn't see the files as "music" and the official Music app and other front-end alternatives like Marvis do not see any of the music on the device. The iPod integration in my car (pre-CarPlay) also doesn't work with Doppler because of this. * The apps don't seem to be developed anymore. I emailed the author weeks ago and he never replied, despite the website saying he replies to messages within a few days. * The apps are very bare bones and missing some features I would like. * There is no native iPad app. The next thing I was hoping would work is an app on macOS that allows me to transfer individual files from the Mac to the mobile devices, but still puts them in the hidden "music" area on the device so that apps can see the files. I learned of [iMazing](https://imazing.com/) which claims to do this, but when I tried the trial, it got stuck attempting to transfer files, and when I was forced to cancel the transfer, nothing had been copied to the device, so I cannot verify it works. Their trial limits you to transferring 50 total music files, which were used up by this aborted transfer, even though it didn't transfer anything. I contacted their support to see if there was some way I could verify that their software works, short of buying it, and they told me there isn't. My experience does not inspire confidence in their software or business practices so I'm reluctant to buy it just to try it further. Are there other Mac apps like iMazing that would allow me to manage the transfer of music files to iOS/iPadOS without using the Finder-based sync? Any other approaches to managing file-based music that I should try? I've spent so much time and energy on this simple thing that should just work.